Polymer/polyol compositions suitable for use in producing polyurethane foams, elastomers and the like are known materials. Such compositions can be produced by polymerizing one or more olefinically unsaturated monomer dissolved or dispersed in a polyol in the presence of a free radical catalyst. These polymer/polyol compositions have the valuable property of imparting to, for example, polyurethane foams produced therefrom, higher load-bearing properties than are imparted by unmodified polyols.
The polymer/polyol compositions that found initial commercial acceptance were primarily compositions produced from polyols and acrylonitrile. Such compositions were somewhat higher in viscosity than desired in some applications. Further, such compositions were primarily used commercially in producing foams under conditions such that the heat generated during foaming was readily dissipated (e.g.--the foams were of relatively thin cross-section) or under conditions such that relatively little heat was generated during foaming. When polyurethane foams were produced under conditions such that the heat generated during foaming was not readily dissipated, severe foam scorching usually resulted. Later, polymer/polyol compositions produced from acrylonitrile-methymethacrylate mixtures were commercialized and were convertible to polyurethane foams having reduced scorch.
More recently, polymer/polyol compositions produced from polyols and acrylonitrile-styrene mixtures have been used commercially. The copending Priest application identified herein provides an improved (semi-batch or continuous) process for forming such polymer/polyols which include, in general, maintaining a low monomer concentration throughout the reaction mixture during the process. The Priest polymer/polyols produced have low viscosities. In addition, the Priest polymer/polyols can be converted to low density, water-blown polyurethane foams having reduced scorch, especially at relatively low acrylonitrile to styrene ratios.
Among the known commercial polymer/polyol compositions produced from acrylonitrile-styrene mixtures is a composition consisting essentially of about 77.5 weight percent of a polol having a molecular weight of about 5600 and about 22.5 weight percent of an acrylonitrile/styrene polymer wherein the acrylonitrile/styrene weight ratio is about 40/60 and having a filterability (as defined below) from 7 to 52 percent. Another such composition consists essentially of about 79.1 weight percent polyol having a molecular weight of about 3400 and about 20.9 weight percent of an acrylonitrile/styrene polymer wherein the acrylonitrile/styrene weight ratio is about 47/53 and having a filterability of 100 percent. Filterabilities of at least 20 percent indicate adequate stability for some applicatons. These compositions are apparently produced by a semi-batch process using azodiisobutyronitrile as a catalyst and a polyol made employing, inter alia, an allegedly critical source of added unsaturation as disclosed in U.S. Pat. No. 3,823,201. The latter patent does not disclose the filterability of its polymer/polyol compositions. Semi-batch processes, such as those of U.S. Pat. No. 3,823,201, are less desirable for large-scale commercial production than are continuous processes. On the other hand, difficulties are encountered in producing highly stable polymer/polyol compositions continuously from acrylonitrile/styrene mixtures using azodiisobutyronitrile as a catalyst as disclosed in the copending Priest application under some conditions (e.g., using relatively low molecular weight polyols).
The copending Simroth application which has been identified discloses additional and substantial improvements in forming polymer/polyols. This allows the optimization of the polymer content and the usable monomer ratios for a given polyol in providing satisfactory stable polymer/polyols.
Despite these improvements, and while polymer/polyol compositions can be produced from widely varying polymer contents and monomer mixtures using azo-type catalyst such as were generally used in producing the above-mentioned polymer polyols, practical quality control restrictions such as stability (as shown, for example, by filterability) have resulted in commercial limitations insofar as the usable maximum styrene content, the maximum polymer content and the minimum molecular weight for the polyol are concerned.
Some patents in the polymer/polyol field disclose the interchangeable use of azo and peroxide catalysts. Thus, for example, among several catalysts set forth, the copending Priest application lists the half-life for t-butylperoxypivalate and t-butylperoxybutyrate. No examples using such catalysts are, however, included. U.S. Pat. No. 3,418,354 discloses polymerizing monomers in polyols using peroxide catalyst containing a peroxide group linked to a tertiary carbon atom (e.g., ditertiary butyl peroxide) but discloses no specific peroxyester catalyst. Indeed, the only specific "example" of a process for forming a polymer/polyol which utilizes a peroxyester, peroxide-type catalyst of which applicants are aware is shown in Great Britain Pat. No. 1,321,679 which discloses in the specification a continuous process for forming an 80/20 acrylonitrile/styrene polymer/polyol having 40 weight percent polymer with a polyether polyol having a molecular weight of 4,000 and a catalyst of azodiisobutyronitrile or tertiary butyl peroctoate. However, in all the working Examples, including one corresponding to this process, an azo catalyst was used.
The use of azo-type catalysts presents processing difficulties due to the solid nature of the catalysts. Also, a toxic, by-product residue is formed. And, as has been described herein, there are limitations which restrict in a practical, commercial sense the polymer/polyol compositions which can be provided.
It has been theorized that the stability of polymer/polyols requires the presence of a minor amount of a graft copolymer formed from the polymer and polyol. And, a number of literature references have observed large differences in grafting efficiency between the use of peroxides such as benzoyl peroxide and azobis-isobutyronitrile in certain monomer-polymer systems while others have noted to marked differences.
In the Journal of Cellular Plastics, March, 1966, entitled "Polymer/Polyols; A New Class of Polyurethane Intermediates" by Kuryla et al, there is reported a series of precipitation experiments run to determine any marked differences in the polymer/polyols produced by either benzoyl peroxide or azobis-isobutyronitrile when used as the initiators in the in situ polymerization of acrylonitrile in a propylene oxide trial having a theoretical number average molecular weight of about 3000. The data indicated no significant differences between the polymers isolated and no marked "initiator effect" was observed.
Indeed, it was reported that the azo catalyzed polymer/polyols were found to be much more reactive, and processed better in the making of urethane flexible foams, than those polymer/polyols which were made using a peroxide catalyst. It was observed that apparently residual peroxides remaining in the refined polymer/polyol "poison" the foaming catalysts.
Accordingly, despite the handling difficulties associated with using azo-type catalysts as has been described herein, virtually all of the commercial polymer/polyol compositions have been produced using this type of catalyst. There has been no recognition in the polymer/polyol field that any superior results could be achieved using a peroxide-type catalyst.
Polymer/polyols have been commercially accepted mostly for various molding applications. However, there has been less acceptance in other applications such as slab stock foam where scorch is a problem, reducing the scorch necessitating the use of acrylonitrile/styrene polymer/polyols with low acrylonitrile/styrene ratio.
In producing polymer/polyols for use in certain polyurethane elastomer applications relatively low molecular weight polyols are typically utilized to provide the requisite product stiffness. However, it is difficult to make satisfactorily stable polymer/polyols from such polyols.
Still other applications could desirably utilize polyurethane foams with even higher load-bearing capacities than can be currently provided using available polymer/polyols.